1. Field of the Invention
This invention relates generally to a capacitive probe for inspecting and measuring the amount of wear in a bore at specific locations along the axis of the bore, and specifically a capacitive probe for inspecting and measuring the wear of the rifle lands in relation to the grooves in a bore.
2. Prior Art
The bore of a gun barrel is machined so that the inner surface of the bore is grooved. These grooves are further machined spirally so as to impart an axial rotating motion to a projectile when discharged from the weapon. When so designed, the grooves carve out lands, the raised sections between grooves. When viewed in cross section, the grooves and lands are typically of equal height and number.
The dimensions and structural integrity of the spiral rifling, comprising the grooves and the lands, of a gun barrel are critical to maintaining accurate and precise operation of the weapon and projection of the projectile. However, through prolonged and hard use, the lands may become worn due to friction, erosion, dirt, exposure to the elements, etc. These problems are particularly of concern with automatic-fire weapons. When the lands become worn, the effectiveness and safety of the weapon are compromised. For example, axial rotation imparted to the projectile is decreased, causing the projectile to travel more slowly or to "knuckle-ball". In fighter aircraft, this may create a major problem, as the aircraft may be traveling faster than the projectile, catch up to the projectile, and damage itself.
At present, there is no fast, convenient, accurate, and precise means of assessing the amount of wear in a gun barrel bore. Visual inspection of the gun barrel is one means of assessing the amount of bore wear. However, a significant amount of wear may occur before one is able to visually detect bore wear, for example, by the presence of slick spots in the bore. Actual weapon operation provides another means of determining the potential presence of worn lands. However, this approach, at best, only alerts one to the possibility of worn lands.
An inner micrometer or other measurement gauge provides the best currently available means of measuring the diameter of a gun barrel bore at various points along the axis of the bore. However, this mechanical measurement technique is limited in accuracy due to the necessity of human input to properly align the gauge.
U.S. Pat. No. 4,168,465 to Prince teaches the use of capacitive probes for inspection and measuring defects in fastener holes, namely a tapered capacitive probe for detecting irregular flaws in metal holes. However, that invention is directed to objects which have a relatively smooth surface and is not capable of accurately measuring the amount of wear in a grooved surface. That is, it is incapable of accurately measuring the land-groove disparity.